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Prevention and Control of Influenza ACIP 2013-2014 page 4
Selected morbidity report, January—July 2013 page 14
South Dakota Influenza Epidemiology and Laboratory Surveillance, 2012-2013 Season
National Influenza Surveillance Data
Influenza-like-illness (ILI) in the United States typically begins to increase in late December or early
January and peaks in February most commonly. The 2012-13 influenza season peaked early and was a
moderately severe season, with influenza A (H3N2) viruses predominating. Nationally activity peaked in
late December, and influenza A (H3N2) viruses were most commonly reported through the week ending
February 16, 2013 (week 7). From the week ending February 23, 2013 (week 8), through the end of the
season, influenza B viruses were more commonly reported. The majority of all influenza viruses in
specimens sent to CDC for further antigenic characterization were similar to the components of the 2012-13
Northern Hemisphere vaccine.
The peak percentage of outpatient visits for ILI (6.1%) was one of the highest reported since the system
began in its current format in 1997. The number and rate of influenza-associated hospitalizations among
adults aged ≥65 years during the 2013-13 influenza season are the highest since systematic data collection
on laboratory-confirmed, influenza-associated hospitalization in adults began in the 2005-06 season.
Hospitalization rates for those aged ≥65 were 191 per 100,000 population, two and a half times the highest
rate previously reported for this age group. With the exception of the 2009 H1N1 pandemic, the number of
influenza-associated pediatric deaths reported to CDC for the 2012-23 season was the highest reported
since data collection began in 2004. Reported pneumonia and influenza mortality exceeded the epidemic
threshold for 13 consecutive weeks. Based on the percentage of specimens testing positive for influenza, the
peak of influenza activity for the 2012-13 season, occurring during the week ending December 29, 2012
(week 52), was similar to the 2003-04 season and was the earliest since the 2009 H1N1 pandemic, when
activity peaked during the week ending October 24, 2009 (week 42).
On March 31, 2013, Chinese health authorities reported a novel avian influenza A (H7N9) virus causing
human infection. As of June 7, 2013, 132 cases have been confirmed; many of the infected people are
reported to have had close contact with poultry. The virus has only been seen in mainland China and
Taiwan; no cases have been reported in the United States. Unlike the variant influenza A (H3N2)v virus
associated with swine exposure at agriculture fairs in the United States which generally caused mild illness,
the avian influenza A (H7N9) virus has caused severe illness in the majority of cases in humans, and
approximately 27% of identified cases have been fatal.
VOLUME 25 NUMBER 4 SEPTEMBER 2013

Prevention and Control of Influenza ACIP 2013-2014 page 4
Selected morbidity report, January—July 2013 page 14
South Dakota Influenza Epidemiology and Laboratory Surveillance, 2012-2013 Season
National Influenza Surveillance Data
Influenza-like-illness (ILI) in the United States typically begins to increase in late December or early
January and peaks in February most commonly. The 2012-13 influenza season peaked early and was a
moderately severe season, with influenza A (H3N2) viruses predominating. Nationally activity peaked in
late December, and influenza A (H3N2) viruses were most commonly reported through the week ending
February 16, 2013 (week 7). From the week ending February 23, 2013 (week 8), through the end of the
season, influenza B viruses were more commonly reported. The majority of all influenza viruses in
specimens sent to CDC for further antigenic characterization were similar to the components of the 2012-13
Northern Hemisphere vaccine.
The peak percentage of outpatient visits for ILI (6.1%) was one of the highest reported since the system
began in its current format in 1997. The number and rate of influenza-associated hospitalizations among
adults aged ≥65 years during the 2013-13 influenza season are the highest since systematic data collection
on laboratory-confirmed, influenza-associated hospitalization in adults began in the 2005-06 season.
Hospitalization rates for those aged ≥65 were 191 per 100,000 population, two and a half times the highest
rate previously reported for this age group. With the exception of the 2009 H1N1 pandemic, the number of
influenza-associated pediatric deaths reported to CDC for the 2012-23 season was the highest reported
since data collection began in 2004. Reported pneumonia and influenza mortality exceeded the epidemic
threshold for 13 consecutive weeks. Based on the percentage of specimens testing positive for influenza, the
peak of influenza activity for the 2012-13 season, occurring during the week ending December 29, 2012
(week 52), was similar to the 2003-04 season and was the earliest since the 2009 H1N1 pandemic, when
activity peaked during the week ending October 24, 2009 (week 42).
On March 31, 2013, Chinese health authorities reported a novel avian influenza A (H7N9) virus causing
human infection. As of June 7, 2013, 132 cases have been confirmed; many of the infected people are
reported to have had close contact with poultry. The virus has only been seen in mainland China and
Taiwan; no cases have been reported in the United States. Unlike the variant influenza A (H3N2)v virus
associated with swine exposure at agriculture fairs in the United States which generally caused mild illness,
the avian influenza A (H7N9) virus has caused severe illness in the majority of cases in humans, and
approximately 27% of identified cases have been fatal.
VOLUME 25 NUMBER 4 SEPTEMBER 2013

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